The salivary peroxidase system is one of the antibody-independent defense mechanisms in human saliva. Salivary peroxidase catalyzes the peroxidation of thiocyanate to give oxidized forms which are potent inhibitors of bacterial metabolism but are non-toxic to host cells. The reactions catalyzed by the system also protect the host from accumulations of the toxic products of oxygen reduction. Our knowledge of the biochemical and antimicrobial mechansims by which the salivary peroxidase system functions has expanded significantly during the last decade. However, the specific relationships between the biochemical properties of the system and oral health have yet to be established and many fundamental questions remain unanswered. What is the structure of salivary peroxidase? What are the mechanisms of its interactions with other proteins in saliva? Do these interactions have any biological significance? What are the natural substrates (other than halides and thiocyanate) of the enzyme? How do fluoride and chloride affect the system? Does the system participate in any reactions toxic to the host? We have designed this component program to provide answers to these questions. As our fundamental knowledge of the biochemistry of the salivary peroxidase system expands, we will be able to understand more completely the various roles which the system may play in defense against oral diseases. We are able to propose this detailed fundamental study because we can now purify to homogeniety quantities of human salivary peroxidase sufficient for the biochemical and various kinetic studies. This preparation also provides us with the necessary reagent to initiate molecular cloning studies. Monoclonal and polyclonal antibodies will be prepared against the enzyme and a related molecule, bovine lactoperoxidase. Using the antibodies and synthetic oligonucleotides it will be possible now to isolate a cDNA clone of salivary peroxidase. The oligosaccharide composition of salivary peroxidase will be determined by convential methods. Recently, it has been demonstrated that bovine lactoperoxidase and its intermediate compounds may react with hydrogen peroxide in a Fenton-like sequence of reactions to generate the highly toxic hydroxyl radical. In order to evaluate the possibility that salivary peroxidse may particiapte in similar toxic reactions, we propose to carry out detailed kinetic studies of these salivary peroxide intermediates. Of particular interest is the study related to interaction between salivary peroxidase and other proteins found in saliva. The effects of these interactions on the glucose metabolism of oral streptococci will be studied. Other important basic aspects of the molecular and cellular biology of salivary peroxidase will also be examined, including its biosynthesis and processing from precursor forms to a mature, fully glycosylated enzyme.